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post #1 of 15 (permalink) Old 07-15-2004, 01:15 PM Thread Starter
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Exclamation Petcock

(this was originally posted by Lance Ostiguy on Yahoo)

I've discovered the petcock actually has 2 valves designed in it. I don't mean the "reserve" or "on" as being the two. There is a simple *check value* located as part of the vacuum tube fitting to the side of the carb. The part you can see as the brass nipple on the bottom of the petcock contains this check value. The check value is there to protect the rubber diaphram in the petcock body from rupturing if the engine backfires (at least this is what I think) and turning you into charcoal. The check valve only works (is open) in one direction, a vaccum. Perhaps, these valves don't function properly with the safety device built into the petcock whenever the fuel pressure in the tank is low? Maybe it's a combination of dirt/wear too? You may want to look at the valve to see if it works freely? I had my petcock dissassembled and noticed I could open the check valve when vacuum was applied to the brass nipple. BTW- No I'm not going to admit to sucking on it. That info is private and only for me and my bike! hehe. Anyways, if
you blow into the nipple you can see that the check valve loses
and no air will pass by it (towards the rubber diaphram). If you're not familiar with check valves, people who have aquariums and air pumps can help you. But it's very simple. A spring and plunger is all what it is. Perhaps the plunger is jammed or sticking at times, thereby shutting off the vacuum to the petcock and gas to the carb bowls. As a simple fix, try shooting some WD40 or such, into the tiny hole in the brass nipple using the red thingy after taking the vacuum tube off. I WOUNLDN'T suggest you discard or bypass the valve altogether, because you're bike might turn into a ball of flame if the engine should backfire, etc.
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post #2 of 15 (permalink) Old 09-04-2004, 06:44 PM
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Unhappy Petcock leaking

*sigh*, yet something else to fix on my bike. Seems like I ride it for
one day, wrench it for seven...

Got home after an 80 mile ride to some dealers in the area, the new big
bikes still don't appeal to me.
Anyway I smelled gas, raw gas. So I went into the garage to get a light
and a rag, I come out and I notice some drips on my left floorboard, yep
gas. I thought it was a loose fuel line, but its apparently not. It
seems that the front arm coming off the petcock is getting wet with gas
from the area where it comes out of the petcock.

I can't see any cracks anywhere. But I looked at the fiche.
http://tinyurl.com/5vhxf I don't see any seals in the diagrams for the
two fuel flow arms that come out of the main body. So I am wondering
if I can rebuild it or if I need to completely replace it?

Thanks
RB

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post #3 of 15 (permalink) Old 11-27-2004, 08:30 PM
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Re: Petcock

I just rebuilt mine last night.There was nothing in the rebuild kit for the arms.From what I could see there was not any seals for it.They are not meant to come apart.Rebuild kit was $23.00 and a used petcock in Phx was $20.00.Used petcocks are not guaranteed.
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post #4 of 15 (permalink) Old 11-29-2004, 08:46 AM
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Re: Petcock

Yep, I took mine apart as far as I could. Grambo had post a while back on the other board that he has had this problem in the past. After I took my tank off, adjusted the fuel tubes some, and put the tank back on, the leak went away. if the pressure on the arms is just right they leak, if you relieve it, they stop leaking... go figure... most annoying...

RB

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post #5 of 15 (permalink) Old 09-04-2005, 07:53 PM
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Question Re: Petcock

Quote:
Originally Posted by UncleGomer
(this was originally posted by Lance Ostiguy on Yahoo)

I've discovered the petcock actually has 2 valves designed in it. I don't mean the "reserve" or "on" as being the two. There is a simple *check value* located as part of the vacuum tube fitting to the side of the carb. The part you can see as the brass nipple on the bottom of the petcock contains this check value. The check value is there to protect the rubber diaphram in the petcock body from rupturing if the engine backfires (at least this is what I think) and turning you into charcoal. The check valve only works (is open) in one direction, a vaccum. Perhaps, these valves don't function properly with the safety device built into the petcock whenever the fuel pressure in the tank is low? Maybe it's a combination of dirt/wear too? You may want to look at the valve to see if it works freely? I had my petcock dissassembled and noticed I could open the check valve when vacuum was applied to the brass nipple. BTW- No I'm not going to admit to sucking on it. That info is private and only for me and my bike! hehe. Anyways, if
you blow into the nipple you can see that the check valve loses
and no air will pass by it (towards the rubber diaphram). If you're not familiar with check valves, people who have aquariums and air pumps can help you. But it's very simple. A spring and plunger is all what it is. Perhaps the plunger is jammed or sticking at times, thereby shutting off the vacuum to the petcock and gas to the carb bowls. As a simple fix, try shooting some WD40 or such, into the tiny hole in the brass nipple using the red thingy after taking the vacuum tube off. I WOUNLDN'T suggest you discard or bypass the valve altogether, because you're bike might turn into a ball of flame if the engine should backfire, etc.
hi uncle ; having read your post i'm still confused as to what happened in my situation with the fuel supply valve on my 2001 vn 750. i had parked my bike in the garage (with a full tank of gas ) for about a week . i tried starting it to take a spin . it cranked and cranked no start . checked for spark was ok. did'nt smell any gas .i drained the tank removed tank and dismantled the shut off valve expecting to find dirt in the filters . everthing was clean as a whistle .reinstalled tank and tried again still no start. i squirted some gas in rear carb and tried again it fired right up ad since starts every time now. my question is ; it normal for carbs to dry out in a week ? and what prevented the fuel to be draw into the carbs while cranking ? i have read some leave the valve on all the time. i have been turning the valve to off when parking between rides.worried this might happen after a shut down while on the road. any ideas as to what happened? one other thought .you said you think the vacuum causes the diaphram to act as a safety feature to prevent a back fire to ignite the fuel tank. my thoughts are the vacuum controls the flow of fuel through the valve . i say this because the kaw shop book says if the valve allows fuel to flow when it is on or in the res position without engine running,replace the damaged gasket or ''o'' ring. under fuel section page 2-27 service manual .regards ken smith
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post #6 of 15 (permalink) Old 03-26-2006, 10:03 AM
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My pet cock was leaking and I took it off and rebuilt it buy replacing the o-rings and Cleaning it up. Now it is not leaking. Go to your dealer and see if they can get the o-rings. It is very easy to do. But you do have to take the tank off.

Last edited by 750 FREAK; 03-28-2006 at 06:53 PM.
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post #7 of 15 (permalink) Old 03-27-2006, 10:16 AM
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I thought my petcock was leaking, but I later realized it was a missing hose clamp on one of the lines. But I still have the Orings should I decide to rebuild it. So, those little "arms" on the sides of the valve aren't supposed to come off?
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post #8 of 15 (permalink) Old 03-28-2006, 06:52 PM
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Quote:
Originally Posted by InsuredDisaster
I thought my petcock was leaking, but I later realized it was a missing hose clamp on one of the lines. But I still have the Orings should I decide to rebuild it. So, those little "arms" on the sides of the valve aren't supposed to come off?
Yes I think you should if it is an older bike. And The little arms i thought wer supposed to come off and Loosened mine by accident and now it is leaking a tiny bit. What year is yours?
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post #9 of 15 (permalink) Old 03-28-2006, 09:14 PM
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Mine's a 90. I just pulled the little arms straight out with the lines still attached, and reconnected them several times. No leaks to report. Is this bad?
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post #10 of 15 (permalink) Old 03-29-2006, 11:53 AM
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I wouldn't say that it is bad if it is not leakng. Being a '90, You may want to rebuild it if it is leaking. If not, then just leave it alone.

'86 Vulcan 750.
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